It is proposed to define the conformational changes in the repressor protein which are involved in the depression of a gene by an inducer on the basis of high resolution Nuclear Magnetic Resonance (NMR) studies. The lac-repressor protein of E. coli, with isopropyl-l-thio-beta-D-galactoside (IPTG) and other galactose derivatives as inducers and the appropriate operator DNA are to be used as a model system. The preparation of selectively deuterated analogs of the repressor should permit a complete analysis of its proton NMR spectrum, as previously demonstrated in the case of the enzyme staphylococcal nuclease, and in part on the (tyr H) repressor analog prepared in the current study. From the spectral changes accompanying inducer and operator binding, it will be possible to infer the nature of the structural changes which constitute the mechanism of derepression. Bibliographic references: Cozzone, Patrick J., Opella, Stanley J., Jardetzky, Oleg, Berthou, Jean, and Jolles, Pierre, "Detection of New Temperatue-Dependent Conformational Transition in Lysozyme by Carbon-13 Nuclear Magnetic Resonance Spectroscopy." Proc. Nat. Acad. Sci. USA, Vol. 72, No. 5, pp. 2095-2098 (May, 1975). Huston, James, S., Moo-Penn, Winston F., Bechtel, Katherine C., and Jardetzky, Oleg, "Characterization of the Lac-Repressor Species Produced by Limited Tryptic Cleavage," Biochem. Biophys, Res. Comm., Vol. 61, No. 2, pp. 441-447 (1974).